1. Field of the Invention
The present invention relates to a heat transfer member, and to a heat transfer assembly including such a member and a semiconductor element. It is particularly, but not exclusively, concerned with a heat transfer member for use in immersion cooling of a semiconductor element.
2. Summary of the Prior Art
A recognised problem in the operation of a semiconductor element, particularly a LSI semiconductor chip, is to ensure that the semiconductor element does not overheat. One way of preventing overheating is to immerse the semiconductor element in a non-conducting, which liquid can then transport heat away from the semiconductor element. Such a technique is known as immersion cooling.
However, in such an arrangement, it is important to ensure satisfactory heat transfer from the semiconductor element to the liquid, and therefore a suitable heat transfer member should be connected to the semiconductor element.
U.S. Pat. No. 3,706,127 discloses an arrangement in which a large number of dendrites (needle-like metal parts) are formed on a surface of the semiconductor element by a suitable metallurgical process. The dendrites are heated when the semiconductor element operates, and therefore the dendrites may act to transfer heat away from the semiconductor element to the surrounding liquid. Since the dendrites have a large number of spaces therebetween, and since the dendrites are believed to have a surface structure with depressions which form bubble-forming nuclei, heat generated in the semiconductor element can rapidly be removed in the form of vapour bubbles of the liquid.
An alternative arrangement is disclosed in JP-A-60-229353. This arrangement will now be discussed in more detail with reference to FIG. 1 of the accompanying drawings. FIG. 1 illustrates a heat transfer assembly in which a heat transfer member 4 is mounted on a semiconductor element 5, which element 5 is itself mounted on a base 6 of e.g. Al.sub.2 O.sub.3. The heat transfer member 4 comprises a plurality of solid layers 7, stacked to form a laminate unit, with that unit being mounted on the semiconductor element 5 via a mounting sheet 8. As can be seen from FIG. 1, the layers 7 have grooves 9 and 9a formed in opposed surfaces thereof, with the grooves 9 and 9a extending generally perpendicular to each other. When the assembly shown in FIG. 1 is immersed in liquid, the liquid enters the grooves 9, 9a, and efficient heat transfer can occur.